# Self Numbers

A Number N is said to be Self Number if it can not be written as M + sum of digits of M for any M.

The first few Self numbers are:

1, 3, 5, 7, 9, 20, 31, 42…………….

### Check if N is a Self number

Given an integer N, the task is to find if this number is Self number or not.

Examples:

Input: N = 3
Output: Yes
Explanation:
1 + sumofDigits(1) = 1
2 + sumofDigits(2) = 4
3 + sumofDigits(3) = 6
Hence 3 can not be written as
m + sum of digits of m for any m.

Input: N = 4
Output: No
2 + sumodDigits(2) = 4

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The idea is to iterate from 1 to N and for each number check that sum of its value and sum of its digit is equal to N or not. If yes then the number is not a self number. Otherwise, the number is a self number.

For Example:

if N = 3

// Check for every number
// from 1 to N
1 + sumofDigits(1) = 1
2 + sumofDigits(2) = 4
3 + sumofDigits(3) = 6

Hence 3 can not be written as
M + sum of digits of M for any M.

Below is the implementation of the above approach:

## C++

 `// C++ implementation to check if the ` `// number is a self number or not ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function to find the sum of ` `// digits of a number N ` `int` `getSum(``int` `n) ` `{ ` `    ``int` `sum = 0; ` `    ``while` `(n != 0) { ` `        ``sum = sum + n % 10; ` `        ``n = n / 10; ` `    ``} ` `    ``return` `sum; ` `} ` ` `  `// Function to check for Self number ` `bool` `isSelfNum(``int` `n) ` `{ ` `    ``for` `(``int` `m = 1; m <= n; m++) { ` `        ``if` `(m + getSum(m) == n) ` `            ``return` `false``; ` `    ``} ` `    ``return` `true``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `n = 20; ` ` `  `    ``if` `(isSelfNum(n)) { ` `        ``cout << ``"Yes"``; ` `    ``} ` `    ``else` `{ ` `        ``cout << ``"No"``; ` `    ``} ` `    ``return` `0; ` `} `

## Java

 `// Java implementation to check if the ` `// number is a self number or not ` `class` `GFG{ ` `     `  `// Function to find the sum  ` `// of digits of a number N ` `static` `int` `getSum(``int` `n) ` `{ ` `    ``int` `sum = ``0``; ` `    ``while` `(n != ``0``) ` `    ``{ ` `        ``sum = sum + n % ``10``; ` `        ``n = n / ``10``; ` `    ``} ` `    ``return` `sum; ` `} ` ` `  `// Function to check for Self number ` `static` `boolean` `isSelfNum(``int` `n) ` `{ ` `    ``for``(``int` `m = ``1``; m <= n; m++) ` `    ``{ ` `       ``if` `(m + getSum(m) == n) ` `           ``return` `false``; ` `    ``} ` `    ``return` `true``; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``int` `n = ``20``; ` ` `  `    ``if` `(isSelfNum(n))  ` `    ``{ ` `        ``System.out.println(``"Yes"``); ` `    ``} ` `    ``else` `    ``{ ` `        ``System.out.println(``"No"``); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed by Ritik Bansal `

## Python3

 `# Python3 implementation to check if the ` `# number is a self number or not ` ` `  `# Function to find the sum of ` `# digits of a number N ` `def` `getSum(n): ` ` `  `    ``sum1 ``=` `0``; ` `    ``while` `(n !``=` `0``): ` `        ``sum1 ``=` `sum1 ``+` `n ``%` `10``; ` `        ``n ``=` `n ``/``/` `10``; ` `     `  `    ``return` `sum1; ` ` `  `# Function to check for Self number ` `def` `isSelfNum(n): ` ` `  `    ``for` `m ``in` `range``(``1``, n ``+` `1``): ` `        ``if` `(m ``+` `getSum(m) ``=``=` `n): ` `            ``return` `False``; ` `     `  `    ``return` `True``; ` ` `  `# Driver code ` `n ``=` `20``; ` ` `  `if` `(isSelfNum(n)): ` `    ``print``(``"Yes"``); ` ` `  `else``: ` `    ``print``(``"No"``); ` ` `  `# This code is contributed by Code_Mech `

## C#

 `// C# implementation to check if the ` `// number is a self number or not ` `using` `System; ` `class` `GFG{ ` `     `  `// Function to find the sum  ` `// of digits of a number N ` `static` `int` `getSum(``int` `n) ` `{ ` `    ``int` `sum = 0; ` `    ``while` `(n != 0) ` `    ``{ ` `        ``sum = sum + n % 10; ` `        ``n = n / 10; ` `    ``} ` `    ``return` `sum; ` `} ` ` `  `// Function to check for Self number ` `static` `bool` `isSelfNum(``int` `n) ` `{ ` `    ``for``(``int` `m = 1; m <= n; m++) ` `    ``{ ` `       ``if` `(m + getSum(m) == n) ` `           ``return` `false``; ` `    ``} ` `    ``return` `true``; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main() ` `{ ` `    ``int` `n = 20; ` ` `  `    ``if` `(isSelfNum(n))  ` `    ``{ ` `        ``Console.Write(``"Yes"``); ` `    ``} ` `    ``else` `    ``{ ` `        ``Console.Write(``"No"``); ` `    ``} ` `} ` `} ` ` `  `// This code is contributed by Code_Mech `

Output:

```Yes
```

References: https://en.wikipedia.org/wiki/Self_number

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